Multi-stage carburetor



United States Patent 3,085,790 MULTI-STAGE CARBURETOR Melvin F. Sterner, Bloomfield Hills, Mich, assignor to Holley Carburetor Company, Van Dyke, Mich, a corporation of Michigan Filed Oct. 5, 1959, Ser. No. 844,248 6 Claims. (Cl. 26123) This invention relates to carburetors for internal combustion engines and more specifically to those carburetors which are capable of multi-stage operation and which have their secondary throttle valve opened by vacuum responsive means.

The present trend in engine design is towards larger engines requiring greater air flows. Consequently, as a result of this trend, the throat diameters of the venturis within the carburetor induction passage have to be made as large as possible so as not to excessively restrict any air flow therethrough.

In multistage carburetors wherein the secondary throttle is actuated by vacuum responsive means, it is conven tional practice to provide conduit means pneumatically connecting the vacuum responsive means to a source of vacuum as that existing at the throat of the venturi within the primary induction passage. However, as a result of maintaining the venturi sizes at a maximum, the effective vacuum force of the air flow past the venturi is materially reduced. The degree of reduction of the vacuum force is usually to such an extent that in order to insure that the secondary throttle will become fully opened by a particular time, initial opening of the secondary throttle valve must be started well in advance of the time that any secondary throttle opening is desired.

Attempts have been made in the past to overcome this undesirable characteristic of early secondary throttle opening. Among these attempts has been the method of pro viding a conduit which communicates with both the primary and secondary induction passages venturis. This particular method \Was partially successful in that the initial opening of the secondary throttle could be delayed a little. However, this proposed method, while partially solving one problem, introduced a more serious and new problem, that being of secondary throttle hunting.

Hunting is that characteristic of a multi-stage carburetor wherein the secondary throttles are continually lagging and then over-correcting their response to changes in position of the primary throttle. The characteristic of hunting becomes a highly aggravated problem when the carburetor is associated with some automatic engine or vehicle speed governing device which controls speed by automatically positioning the primary throttle.

Accordingly, an object of this invention is to provide means for efifecting a greater degree of flexibility to the control of the secondary throttle valve in a multi-stage carburetor.

Another more specific object of this invention is to provide automatic means for eliminating the problem of hunting in a multi-stage carburetor.

Other objects and advantages of this invention will become apparent when reference is made to the following written description and illustrations wherein:

FIGURE 1 is a side e-levational view of a multi-stage carburetor, partially in cross-section, illustrating one embodiment of the invention.

FIGURE 2. is a fragmentary cross-sectional view of a modification of the invention.

FIGURE 3 is a graph illustrating the comparative performance curves of the invention, as contrasted to those of prior design.

Referring now in greater detail to the drawings, FIG- URE 1 illustrates a multi-stage carburetor 10 having a 3,085,790 Patented Apr. 16, 1963 body portion 12 with primary and secondary induction passages -14 and 16 therethrough and primary and secondary throttle valves 18 and 20 therein adapted to control the flow of combustible mixtures to an engine intake manifold 22. The conventional choke valve 24 mounted on thechoke shaft 30 may be controlled in any suitable manner as by means of linkages 26- and 28 operaitively connected to the choke shaft.

Individual fuel bowls such as the primary fuel bowl 32 and the secondary fuel bowl 34 may be provided to properly supply fuel to the individual induction passages. Although the fuel metering systems are not part of this invention, the main metering system nozzles for the primary and secondary induction passages are illustrated at 36 and 38, respectively.

The primary throttle 18 may be operated manually, as by means of linkages 4i) and 42 operatively connected to the throttle shaft 44. Although it is not illustrated, it is, of course, obvious that the throttle 18 could be controlled by some governor mechanism responsive to either engine or vehicle speed. The secondary throttle valve '20 is posi tioned in accordance with the dictates of the vacuum responsive device 46 as by means of linkages 48 and 50 connected to the secondary throttle shaft 52.

The vacuum responsive device 46 is generally comprised of housing portions 54 and 56 adapted to be secured together by any suitable means in a manner so as to retain a flexible diaphragm member 58 therebetween, thereby forming two general chambers 60 and 62. Chamber 60, which may contain a biasing spring 64 therein urging the diaphragm 58 and linkage 48 in the throttle closing direction, may be exposed to either a source of atmospheric air or to a source of vacuum, as will be more fully explained later in the specification. Chamber 62, however, is permanently vented to the atmosphere as by a vent 66.

A regulating valve 68, which may be of a general spool shape, is slidably received Within a cylindrical chamber 76) which may be formed integrally within the carburetor body '12. One end of the chamber is in constant communication with a source of manifold vacuum as by means of a conduit 72 connecting with the induction passage 14 at some suitable distance downstream of the throttle valve 18. The other end of the chamber 70 is in communication with a source of atmospheric air as by means of the passage 74 and restriction 75. A spring 78 located in chamber 70 urges the valve 68 in a direction in opposition tothat of the manifold vacuum communicated by conduit 72. A spring 80 and an adjustable spring seat 76 may be provided at the opposite end of valve 68 in order to have adjustability of the spring rate and load of the entire system. If desired, a positive stop, in the form of a shoulder portion 71 formed within chamber 70,-can be provided so that valve 63 may abut against it when invthe fully downward position.

A conduit 82 provides communication between the chamber 60, of the device 46, and the chamber 70. A second conduit 84 provides communication between the vacuum existing at the throat of the venturi 86 and the chamber 70. It should be noted, however, that when the valve 68 is in a position substantially as illustrated in FIGURE 1, that no communication exists between the conduits 82 and 84,. When the valve 68 is in the position shown, the conduit 82 communicates between the chamber 60 and a source of atmospheric air as by passage 74.

Operation manifold vacuum then causes the valve 68 to assume a position as illustrated thereby preventing any communication between the chamber 60 and venturi 86.

As the throttle 18 progressively opens, the manifold vacuum applied to the valve 68 diminishes, allowing the valve 68 to rise upwardly some amount. When the throttle valve 18 has been opened some sufiicient amount, the manifold vacuum will be reduced to such a degree permitting the regulating valve 68 to move upwardly to such a position whereby communication between conduits 82 and 84 is made possible. The venturi vacuum existing then at the venturi throat is directed to chamber 60 causing the diaphragm 58 to move against the force of spring 64- and thereby open the secondary throttle.

It is, of course, evident that two conditions must always be present before the secondary throttle will be opened; first, the manifold vacuum must be reduced to a certain predetermined value and secondly, there must be a sufficient air flow past the venturi throat 86 at the time the manifold vacuum attains this particular value.

In other words, if the engine is operating at curb idle which may be approximately 500 rpm. and the primary throttle is suddenly moved to wide open position, the secondary throttle will not be opened even though the manifold vacuum has been reduced and there is communication between conduits 82 and 84. The reason for this is that at these low r.p.m.s there is not a suflicient air flow past the throat 86 to actuate diaphragm 58.

The regulating valve 68 as illustrated in FIGURE 1 is provided with two cylindrical valving portions 67 and 69. In the embodiment of FIGURE 1, the width of the cylindrical portion 67 is of such a length as to enable it to close off the entire orifice 73 as the valve 68 moves upwardly. This feature will eliminate any bleeding of vacuum around the portion 67 and result in making the diaphragm 58 responsive to the full venturi vacuum existing at the throat 86 when communication between conduits 82 and 84 is finally achieved. Curve C of FIGURE 3 illustrates the performance curve of such a construction.

The second valving portion 69 is displaced a certain distance away from the portion 67 which will enable the portion 69 to completely cover orifice 83 after the upper portion 67 has completed its function of providing communication between conduits 82 and 84. By having the portion 69 so located with respect to 67, it is possible to control the response of the diaphragm 58 during all periods of engine operation, even wide open throttle conditions. For example, it may be desirable in a particular engine to have the secondary throttles operate only during those periods when the engine manifold vacuum is less than 7.0 inches of mercury but greater than 1.0 inch of mercury. If such was the case, then the valve portion 67 would complete the communication between conduits 82 and 84 by at least partially passing above orifice 73 when a manifold vacuum of 7.0 inches of mercury was attained. Accordingly, as the vacuum continued to decrease, the regulating valve 68 would continue to move upwardly until valving portion 69 closed off orifice 83 at the time that the manifold vacuum was at a value of 1.0 inch of mercury.

Additionally, it should be noted that as valving portion 69 closes off the orifice 83, valving portion 67 simultaneously starts to complete the communication between conduit 82 and conduit 74 which, as was previously stated, communicates with a source of atmospheric air. The atmospheric air admitted in this manner enters chamber 60 of the pressure responsive device 46, equalizing the pressure on both sides of the diaphragm 58. This allows linkage 48 to move downwardly under the force of the spring 64, thus pivoting linkage '50 and closing the secondary throttle valve 20.

FIGURE 2 illustrates a modification of the invention whereby the responsiveness of the secondary throttle may be changed from that as indicated by curve C of FIG- URE 3 to either curve D or E. This is accomplished by making the valving portion 67 slightly shorter than the orifice 73 so that the orifice could never be completely closed by the valve portion 67. By so doing, some atmospheric air is bled by the valve 67' before the diaphragm 58 can respond. This causes the performance curve to become a little more gradual during the initial opening stages, instead of instantaneous as indicated by curve C.

From the preceding, it should be evident that the time of initial opening of the secondary throttle valve can be set at any particular time as desired and yet obtain full secondary throttle opening when required. This is accomplished, of course, by the proper selection and adjustment of springs 64, 78, and 80.

Additionally, the invention is not troubled with the problem of hunting since when the primary throttle 18 is caused to close, either manually or by some governor means, the manifold vacuum may increase to such a degree causing the valve 68 to assume a position substantially as illustrated, thereby venting the chamber to the atmosphere by means of conduit 74. The restriction 75 may be included in order to prevent a sudden venting of the chamber 60, but rather provide a dashpot effect.

FIGURE 3, as previously identified, illustrates comparative performances of multi-stage carburetors of prior design as compared to the invention. For example, curve A designates a multi-stage carburetor having the vacuum responsive device which positions the secondary throttle valve in constant communication with the primary venturi throat; curve B illustrates the performance of a multi-stage carburetor wherein the vacuum responsive device as 46 is in constant communication with both the primary and secondary induction passage venturi vacuum; curve C illustrates the secondary response in the embodiment of FIGURE 1, and curves D and E illustrate other possible performance curves of a multi-stage carburetor constructed in accordance with the teachings of this invention as disclosed in the modification of FIG- URE 2.

Although only two embodiments of the invention have been disclosed and described, it is apparent that other modifications are possible within the scope of the ap pended claims.

What I claim as my invention is:

1. In a multi-stage carburetor for an internal combustion engine equipped with an intake manifold having primary and secondary induction passages, a venturi in each of said induction passages and a pair of throttle valves, one in each of said passages, manual means for controlling the throttle valve of one of said induction passages, pressure responsive means connected with the other of said throttle valves and responsive to the pressure within said primary venturi for controlling the last mentioned throttle valve, and valve means responsive to engine intake manifold vacuum in the primary induction passage downstream of the throttle for controlling the degree of communication between said pressure responsive means and said primary venturi only.

2. In a multi-stage carburetor for an internal combustion engine including a body, primary and secondary induction passages having venturis therein and a throttle valve in each passage, manual means for controlling the first of said throttle valves, pressure responsive means for automatically opening the second of said throttle valves in accordance with the pressure created by air flow past said first throttle valve, a chamber formed within said body, an atmospheric vent connected to said chamber, first conduit means providing communication between said chamber and said pressure responsive means, second conduit means providing communication between said chamber and a source of manifold vacuum in the primary induction passage downstream of said primary throttle, third conduit means providing communication between said chamber and the venturi of said primary passage, and a spring biased regulating valve within said chamber at all times upstream of said second conduit means, said valve in one position providing communication between said vent and said pressure responsive device, and responsive to engine vacuum downstream of the primary throttle thereby to move to a second position to provide communication between said pressure responsive device and the venturi in said primary induction passage.

3. In a multistage carburetor for an internal combustion engine including a body, primary and secondary induction passages having venturis therein and a throttle valve in each passage, manual means for controlling the first of said throttle valves, pressure responsive means for automatically opening the second of said throttle valves in accordance with the pressure created by air flow past said first throttle valve, a chamber formed within said body, an atmospheric vent connected to said chamber, first conduit means providing communication between said chamber and said pressure responsive means, second conduit means providing communication between said chamber and a source of manifold vacuum in the primary induction passage downstream of said primary throttle, third conduit means providing communication between said chamber and the venturi of said primary passage, and a spring biased regulating valve within said chamber at all times upstream of said second conduit means, said valve being moved to a first position above a predetermined maximum engine vacuum to provide communication between said vent and said pressure responsive device, and responsive to engine vacuum downstream of the primary throttle thereby to move to a second position to provide communication between said pressure responsive device and the venturi in said primary induction passage.

4. A multi-stage carburetor for an internal combustion engine having an intake manifold, comprising a body, a primary and a secondary induction passage formed through said body and adapted to communicate with said intake manifold, primary and secondary throttle valves located in said primary and secondary induction passages, respectively, and adapted to control the flow of combustible mixtures therefrom, manual means for controlling the position of said primary throttle, vacuum responsive means for automatically controlling the position of said secondary throttle valve, a venturi in said primary induction passage, first conduit means leading from said vacuum responsive means and adapted to at times communicate with the throat of said primary venturi, a chamber formed within said body, second conduit means communicating between said chamber and a source of manifold vacuum in the primary induction passage downstream of said primary throttle, an atmospheric vent connected to said chamber, and a spring biased regulating valve located within said chamber at all times upstream of said second conduit means and positioned in accordance with said communicated manifold vacuum for completing the communication between said first conduit means and said venturi throat or said at mospheric vent.

5. In a multi-stage carburetor for an internal combustion engine including a body, primary and secondary induction passages having venturis therein and a throttle valve in each passage, manual means for controlling the first of said throttle valves, pressure responsive means for automatically opening the second of said throttle valves in accordance with the pressure created by air fiow past said first throttle valve, a chamber formed within said body, an atmospheric vent connected to said chamber, first conduit means providing communication between said chamber and said pressure responsive means, second conduit means providing communication between said chamber and a source of manifold vacuum in the primary induction passage downstream of said primary throttle, third conduit means providing communication between said chamber and the venturi of said primary passage, and a spring biased regulating valve Within said chamber at all times upstream of said second conduit means, said valve being moved to a first position at a predetermined minimum engine vacuum to provide communication between said vent and said pressure responsive device and responsive to a predetermined maximum engine vacuum in the primary passage to move to a second position to provide communiction between said vent, said pressure responsive device and said third conduit means.

6. In a multi-stage carburetor for an internal combustion engine including a body, primary and secondary induction passages having venturis therein and a throttle valve in each passage, manual means for controlling the first of said throttle valves, pressure responsive means for automatically opening the second of said throttle valves in accordance with the pressure created by air flow past said first throttle valve, a chamber formed within said body, an atmospheric vent connected to said chamber, first conduit means providing communication between said chamber and said pressure responsive means, second conduit means providing communication between said chamber and a source of manifold vacuum in the primary induction passage downstream of said primary throttle, third conduit means providing communication between said chamber and the venturi of said primary passage, and a spring biased regulating valve within said chamber at all times upstream of said second conduit means, said valve being moved to a first position at a predetermined minimum engine vacuum to provide communication between said vent and said pressure responsive device, and responsive to engine vacuum downstream of the primary throttle thereby to move to a second position to provide communication between said pressure responsive device and the venturi in said primary induction passage.

References Cited in the file of this patent UNITED STATES PATENTS 2,355,716 Ericson et a1 Aug. 15, 1944 2,376,732 Strebinger May 22, 1945 2,390,019 Winkler et a1 Nov. 27, 1945 2,609,806 Winkler Sept. 9, 1952 2,798,703 Carlson et al. July 9, 1957 

1. IN A MULTI-STAGE CARBURETOR FOR AN INTERNAL COMBUSTION ENGINE EQUIPPED WITH AN INTAKE MANIFOLD HAVING PRIMARY AND SECONDARY INDUCTION PASSAGES, A VENTURI IN EACH OF SAID INDUCTION PASSAGES AND A PAIR OF THROTTLE VALVES, ONE IN EACH OF SAID PASSAGES, MANUAL MEANS FOR CONTROLLING THE THROTTLE VALVE OF ONE OF SAID INDUCTION PASSAGES, PRESSURE RESPONSIVE MEANS CONNECTED WITH THE OTHER OF SAID THROTTLE VALVES AND RESPONSIVE TO THE PRESSURE WITHIN SAID PRIMARY VENTURI FOR CONTROLLING THE LAST MENTIONED THROTTLE VALVE, AND VALVE MEANS RESPONSIVE TO ENGINE INTAKE MANIFOLD VACUUM IN THE PRIMARY INDUCTION PASSAGE DOWNSTREAM OF THE THROTTLE FOR CONTROLLING THE DEGREE OF COMMUNICATION BETWEEN SAID PRESSURE RESPONSIVE MEANS AND SAID PRIMARY VENTURI ONLY. 